Linguloidean brachiopods from the Lower Ordovician (Tremadocian) of northwestern Argentina

The new obolid Torobolus subplanus gen. et sp. nov., from the lower Temadocian Devendeus Formation, the new species Libecoviella tilcarensis and Leptembolon argentinum, and Ectenoglossa sp. from upper Tremadocian beds of the Santa Rosita Formation are described and ilustrated. Libecoviella is typical of the upper Tremadocian and Floian strata of the Prague basin (Trenice and Klabava formations, respectively) and it has been reported recently from Australia. Leptembolon has been recorded in the same Bohemian formations, but together with other taxa it forms the Thysanotos-Leptembolon Association present in northern Estonia and a series of high-latitude terranes. The record of Leptembolon and Libecoviella in the high- to temperate-latitude Central Andean region attests for a peri-Gondwanan distribution of these genera. The presence of Bohemian-like obolids in northwestern Argentina suggests a migratory route linking the Central Andean basin with north Gondwana and Perunica along the clastic platforms fringing the North African and Brazilian shieldsFil: Benedetto, Juan Luis Arnaldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Muñoz, Diego Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentin

The eoorthid brachiopod Apheoorthina in the Lower Ordovician of NW Argentina and the dispersal pathways along western Gondwana

The eoorthid brachiopod Apheoorthina is reported for the first time from the Lower Ordovician of NW Argentina. It is represented by a species similar to A. ferrigena from the Tremadocian of the Prague Basin, increasing the faunal affinities between the Central Andean Basin and the South European microcontinents, in particular the Bohemian region (Perunica). Nine out of the fourteen brachiopod genera reported from the Tremadocian of the Central Andean Basin (~64 %) are shared with the Mediterranean region, four of which (~ 28 %) have been recorded in the Prague Basin, and two (Kvania and Apheoorthina) are restricted to the Central Andes and Perunica. Dispersal pathways around Gondwana are analyzed in the light of major factors affecting large-scale distribution of brachiopods (environment, larval capacity for dispersal, oceanic currents).The presence in Apheoorthina aff. ferrigena of a well-preserved larval protegulum measuring 420 μm in width and 210 μm in length strongly suggests that this species had planktotrophic larvae capable of long-distance dispersal. According to recent oceanatmosphere general circulation models for the Ordovician Period, the Central Andean margin was dominated by the cold-water Antarctica Current. Despite the complex nonzonal pattern produced by current deflections around the peri-Gondwanan microcontinents, the general westward circulation sense favoured larval dispersal from the Andean region to North Africa, Avalonia, the Armorican Terrane Assemblage, and Perunica. On the other hand, the eastwards flowing Gondwana Current connected the North Gondwana waters with the South American epicontinental seas, which could explain the reversed migration of some brachiopods.Fil: Muñoz, Diego Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Benedetto, Juan Luis Arnaldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentin

Hydrodynamics of circumbinary accretion: Angular momentum transfer and binary orbital evolution

We carry out 2D viscous hydrodynamical simulations of circumbinary accretion using the AREPO code. We self-consistently compute the accretion flow over a wide range of spatial scales, from the circumbinary disk (CBD) far from the central binary, through accretion streamers, to the disks around individual binary components, resolving the flow down to 2% of the binary separation. We focus on equal-mass binaries with arbitrary eccentricities. We evolve the flow over long (viscous) timescales until a quasi-steady is reached, in which the mass supply rate at large distances $\dot{M}_0$ (assumed constant) equals the time-averaged mass transfer rate across the disk and the total mass accretion rate onto the binary components. This quasi-steady state allows us to compute the secular angular momentum transfer rate onto the binary, $\langle\dot{J}_b\rangle$, and the resulting orbital evolution. Through direct computation of the gravitational and accretion torques on the binary, we find that $\langle\dot{J}_b\rangle$ is consistently positive (i.e., the binary gains angular momentum), with $l_0\equiv\langle\dot{J}_b\rangle/\dot M_0$ in the range of $(0.4-0.8)a_b^2\Omega_b$, depending on the binary eccentricity (where $a_b,~\Omega_b$ are the binary semi-major axis and angular frequency); we also find that this $\langle\dot{J}_b\rangle$ is equal to the net angular momentum current across the CBD, indicating that global angular momentum balance is achieved in our simulations. We compute the time-averaged rate of change of the binary orbital energy for eccentric binaries, and thus obtain the secular rates $\langle\dot a_b\rangle$ and $\langle \dot{e}_b\rangle$. In all cases, $\langle\dot{a}_b\rangle$ is positive, i.e., the binary expands while accreting. We discuss the implications of our results for the merger of supermassive binary black holes and for the formation of close stellar binaries.Comment: 18 pages, 13 figures, 1 table. Accepted for publication in Ap

Suppression of extreme orbital evolution in triple systems with short range forces

The Lidov-Kozai (LK) mechanism plays an important role in the secular evolution of many hierarchical triple systems. The standard LK mechanism consists of large-amplitude oscillations in eccentricity and inclination of a binary subject to the quadrupole potential from an outer perturber. Recent work has shown that when the octupole terms are included in the potential, the inner binary can reach more extreme eccentricities as well as undergo orientation flips. It is known that pericenter precessions due to short-range effects, such as General Relativity and tidal and rotational distortions, can limit the growth of eccentricity and even suppress standard (quadrupolar) LK oscillations, but their effect on the octupole-level LK mechanism has not been fully explored. In this paper, we systematically study how these short-range forces affect the extreme orbital behaviour found in octupole LK cycles. In general, the influence of the octupole potential is confined to a range of initial mutual inclinations Itot centered around 90deg (when the inner binary mass ratio is <<1), with this range expanding with increasing octupole strength. We find that, while the short-range forces do not change the width and location of this "window of influence", they impose a strict upper limit on the maximum achievable eccentricity. This limiting eccentricity can be calculated analytically, and its value holds even for strong octupole potential and for the general case of three comparable masses. Short-range forces also affect orbital flips, progressively reducing the range of Itot within which flips are possible as the intensity of these forces increases.Comment: 20 pages,15 figures, updated to match version published on MNRA

Ingeniería didáctica: solución de problemas mediante sistema de ecuaciones lineales, con estudiantes de noveno grado

Se realiza una investigación de tipo cualitativo en educación matemática, con estudiantes de grado noveno de la institución educativa CASD, para identificar qué esquemas aplican en el desarrollo del concepto “solución de problemas mediante sistema de ecuaciones lineales”. Se implementó la metodología de la ingeniería didáctica (Artigue, Douady, Moreno & Hurtado, 1995). Se realizaron sesiones educativas presenciales y de trabajo extracurricular para cumplir con las cuatro fases de la ingeniería didáctica. Como producto del proceso se contará con una metodología adecuada para implementarla en la institución educativa, que contribuya a mejorar el desempeño académico, innovar los métodos de enseñanza y aprendizaje, con ayuda de las TIC y reducir la pérdida de grados de los estudiantes de básica secundaria

The Rapanui diaspora in Tahiti and the lands of Pamatai (1871-1970)

International audienceWhen commercial flights between Rapa Nui and Tahiti began in 1968, after nearly 70 years of colonial confinement,a new migratory process began from Rapa Nui to Tahiti. This included claims of ownership of the lands of Pamatai,bought 80 years earlier by a group of 25 Rapanui immigrants. For the Rapanui people, the history of the landsof Pamatai evokes a series of memories and forgotten events, genealogical ties, as well as a constant search for alinkage with Tahiti – a “memory of diaspora.”In this paper, I analyze the history of links between Rapanui people and Tahiti and the role of the lands ofPamatai in the Rapanui migration process: the exodus during the nineteenth century, confinement on Easter Island,the broken link with Tahiti, and Rapanui claims for ownership of the lands of Pamatai after the 1970s

Les Rapanui à Tahiti. Histoire de migration, de terres et de parenté

En 1872 les missionnaires catholiques du Sacré Cœur du Picpus quittent l'île de Pâques avec 277 insulaires, soit plus de la moitié de la population. C'est le début de la diaspora Rapanui en Polynésie. Au cours des 10 années suivantes quatre colonies de Rapanui se sont formées en Polynésie : une à Mangaréva, une autre à Moorea et deux à Tahiti. Même si ces colonies ont connu une forte mortalité, les survivants se sont regroupés autour de la mission catholique à Tahiti. En 1887 les missionnaires vendent à vingt-cinq Rapanui un domaine foncier appelé Pamata'i, situé dans l'actuelle commune de Faaa. Cet évènement est au fondement de plus d'un siècle d'histoire de liens entre les Rapanui et Tahiti. Dans cet exposé nous analyserons l'histoire de migration des Rapanui à Tahiti au long du XXème siècle. Au-delà des évènements particuliers, ce qui nous intéresse est de comprendre les liens que les Rapanui ont établis avec les terres de Pamata'i et la place de celles-ci dans leurs flux migratoires en Polynésie. Nous pouvons qualifier ces liens de mémoriels, de parenté et de propriété. En effet, les terres de Pamata'i sont devenues la raison première de la migration et l'installation des Rapanui à Tahiti. Ainsi les récits actuels sur la parenté et notamment la fabrication des généalogies construisent l'argumentaire des revendications de droits sur ces terres. Cette histoire de diaspora nous permettra de comprendre la complexité des flux migratoires entre l'île de Pâques et la Polynésie française et les enjeux d'ordre identitaires, économiques et affectifs dans les rapports que les Rapanui entretiennent avec la Polynésie